Auto-focus system with 2-D or 3-D compensation

ABSTRACT

An optical scanning apparatus and method for scanning a surface of an object is provided. The scanner has an image sensor having a sensor plane and an image data output. An optics system defines an optical path having an axis and a first end whereat a scan object surface is locatable for scanning and a second end at the sensing plane. Preferably, the optics system includes a lens subsystem and a movable mirror for adjusting the length of the optical path. A linear actuator is coupled to the mirror such that movement of the mirror adjusts the focus of an optical image on the image sensor. A linear actuator is also operatively coupled to the image sensor to control the orientation of the plane of the image sensor relative to the optical path axis. When a scan object surface is located at the first end of the optical path at an orientation skewed from a plane orthogonal with the optical path axis at the first path end, the linear actuator orients the sensor plane to a corresponding skewed orientation relative to a plane orthogonal with the optical path axis at the second path end.

The present invention relates to an automatic focusing optical scanningapparatus and method. More particularly, this invention relates to anautomatic focusing apparatus and method with 2-D or 3-D compensation toscan coded symbologies on a package regardless of the packagesorientation on a transporting conveyor.

BACKGROUND

In order to achieve processing automation of packages, it is desirableto be able to scan coded symbologies of a package where the package isbeing transported along a surface, such as a conveyor surface. The needfor efficiency in handling a large volume of packages has become moreapparent with increases in interstate shipping due to Internet commerce.

Prior known optical scanning systems utilize an optical sensor to detectthe coded symbologies located on the package. In general, prior artsystems adjust the position of the lens system relative to the imagesensor to focus the image of the coded symbology on the image sensor.Even if the scanning system locates a coded symbology on a package, ifthe package is skewed with respect to the scanning system, the imagesensor may be unable to focus on the entire coded symbology. This canresult in higher costs for processing.

It is desirable to provide a fast, accurate and cost efficient system toautomatically focus on coded symbologies of a package traveling on aconveyor.

SUMMARY OF THE INVENTION

An optical scanning apparatus and method for scanning a surface of anobject is provided. The scanner has an image sensor having a sensorplane and an image data output. An optics system defines an optical pathhaving an axis and a first end whereat a scan object surface islocatable for scanning and a second end at the sensing plane. The opticssystem includes a lens subsystem and may include a movable mirror foradjusting the length of the optical path. A linear actuator is coupledto the mirror such that movement of the mirror adjusts the focus of anoptical image on the image sensor.

Another linear actuator is also operatively coupled to the image sensorto control the orientation of the plane of the image sensor relative tothe optical path axis. When a scan object surface is located at thefirst end of the optical path at an orientation skewed from a planeorthogonal with the optical path axis at the first path end, the linearactuator orients the sensor plane to a corresponding skewed orientationrelative to a plane orthogonal with the optical path axis at the secondpath end.

Preferably, the sensor linear actuator pivots the image sensor planeabout a central axis of the image sensor plane and the optical path isconfigured such that the optical path axis passes through the centralaxis.

Alternatively, two linear actuators are coupled to the optical sensorfor working cooperatively together to pivot the image sensor plane alonga vertical image axis and a horizontal image axis. Preferably, one ofthe pivot axes of the image sensor plane is a central axis of the imagesensor plane and the optical path is configured such that the opticalpath axis passes through the central axis.

Preferably, the drive system of each linear actuator is coupled to aposition feedback mechanism which outputs data to assist in the controlof the linear actuators. The optical sensor preferably is a CCD/CMOSarea or linear image sensor.

Other objects and advantages will be apparent to a skilled artesian fromthe following description of presently preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a scanning identification station with objectsfor scanning being transported along a conveyor surface.

FIG. 2 is a side schematic view of the apparatus according to theteachings of the present invention.

FIG. 3 is a perspective schematic view of a position controlled imagesensor for the apparatus of FIG. 2.

FIG. 4 is a perspective schematic view of an alternate embodiment of aposition controlled image sensor for the apparatus.

FIG. 5 is a perspective schematic view of an alternate embodiment of aposition controlled image sensor for the apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, wherein like numerals designate like elementsthroughout, FIG. 1 shows a top view of an overall scanning system layoutwhere objects 2, 3 to be scanned are transported on a conveyor surface 4through a scanning zone 5. Preferably, multiple scanners 6–9 monitor thescanning zone 5. Front and back scanners 6, 7 are preferably angled downat the scan surface to scan front, back and top sides. Side scanners arepreferably pointed directly at the left and right sides of the scanningzone 5. Coded symbologies on objects passing through the scan area canbe scanned by any one of the stationed scanners 6–9 so that symbologieson all sides of the objects can be read. However, a single scanner maybe provided, such as for systems where symbologies are only to be readfrom a single given side of a package passing through the scan area 5.

Preferably, the system is designed to scan boxes with flat rectangularsides such as objects 2, 3, with code symbologies on at least one side,but preferably not the bottom side. However, it is possible to provide ascanner for bottom side scanning. As each object 2, 3 enters the scanzone 5, its corresponding front surface 10 and 11, is frequently notperpendicular to the direction of travel of the conveyor 4. If the frontsurface plane 10, 11 of an object 2, 3 is less than about 45 degreesfrom being perpendicular to the direction of travel, the front or backscanner 6, 7 will scan the coded symbologies of the object appearing onthe front or back sides. If, for example as shown with object 3, thefront surface plane of an object is close to 45 degrees from beingperpendicular to the direction of travel, the right or left sidescanners 8, 9 will scan the coded symbologies on the front, back, leftor right sides of the object and the front and back scanners 6, 7 willscan coded symbologies on the object top side.

A conventional package position sensor system 12 is provided in advanceof the symbology scanning area 5. The package position sensor systemdetermines dimensions of the objects 2, 3 and the position and angularorientation of the objects 2, 3 on the conveyor 4. The dimension,position and orientation data of an object 2, 3 is provided from thesensor system 12 to the scanners 6–9 for use in scanning the object 2, 3in the scanning area 5.

Where the front surface planes 10, 11 of an object 2, 3 are notperpendicular to the direction of travel, the scanning of the codedsymbology will not result in a completely focused image of the codedsymbologies using conventional optical path focusing.

As best seen in FIG. 2, an automatic system for focusing an opticalscanning apparatus, such as scanners 6–9, in accordance with the presentinvention is illustrated. The automatic focusing system includes animage sensor 26 and a lens system 22 having a lens 24 with an objectside 24 a and an image side 24 b. The image sensor is preferably a CCDor CMOS area or linear image sensor.

The lens system 22 is located in a fixed position relative to an opticalaxis 21 which is orthogonal to the scanner's reference plane. While thelens system 22 is illustrated as including a single objective lens 24,it will be recognized by those skilled in the art that the lens system22 may include multiple lenses, depending upon the particularapplication.

One or more mirrors 25, 27 are positioned on the image side 24 b of thelens system 22. The mirrors 25, 27 are located such that an imagelocated along the optical axis 21 is reflected by the mirrors to theimage sensor 26 as illustrated, for example, in FIG. 2, generally alonga path normal to the face 26 a of the image sensor.

A linear actuator mechanism 30 is provided to move the mirror 25backward or forward relative to the lens system 22 to change the opticalpath distance to the image plane 26 a relative to the lens system 22 tofocus the image of the object 2. The linear actuator 30 is connected tothe mirror 25 via an arm 32 which is controlled by a linear motor 34. Inthe preferred embodiment, the linear actuator arm 32 is held in place bya suspension system 35. However, those skilled in the art willunderstand that the linear actuator 30 may be constructed as a solenoidor a stepper motor with a lead screw or using any other suitablecontrollable displacement means.

A Linear Variable Differential Transformer (LVDT) 36 or an equivalentdevice provides position feedback for the linear actuator 30 to provideclosed loop position control of the focusing mirror 25. When theactuator 30 is actuated, the arm 32 moves the mirror 25 back and forthin line with the optical axis 21 relative to the lens system 22 and theposition is sensed by the LVDT 36.

Referring to FIG. 3, a supplemental focusing control operative with theimage sensor 26 is illustrated. A linear actuator 29 controls therotation or pitch of the image sensor 26 about a vertical image axis 27.Optionally, two linear actuators 29 are coupled to extending tabs 28 a,28 b, one each, respectively, to pivot the sensor surface 26 about thefixed center axis 27 of the sensor 26, the vertical axis of the imagescorresponding to the center axis 27 of the sensor 26. Each actuator 29preferably includes a LVDT 33 or an equivalent device to provide preciseposition feedback data. Where two actuators 29 are provided, theactuators are preferably operated in tandem to provide equal andopposite movement on respective tabs 28 a, 28 b for providing precisepositioning of the sensor surface 26 a.

When scanning a skewed surface 10 of an object 2, the mirror linearactuator 30 adjusts the distance of the mirror 25 along the optical axis21 until a particular portion of object 10, preferably proximate centeraxis 27, is in focus on the image sensor surface 26 a. The sensor linearactuator 29 rotates the image sensor plane 26 a along the center fixedaxis 27 by pushing or pulling pivot tabs 28 b to match the skew of theobject 2. Accordingly, the plane of the object surface 10 as observedthrough the lens system 22 image sensor 26 becomes in focus on theentire sensor surface 26 a. Such complete focus occurs by utilizing thesupplemental focusing control to position the sensor plane 26 a in anorientation which is skewed to correspond to the skew of the objectsurface 10 from respective planes orthogonal with the optical axis atopposing ends of the optical image path.

The control of the actuators is in a conventional manner primarily basedon data generated by the package position sensor system 12, with theLVDTs or equivalent devices providing feedback for closed looppositioning.

Referring to FIG. 4, a second embodiment of the supplemental automaticfocusing control is shown. In this embodiment, the image sensor 26 ismounted for rotational movement about two axes 59, 69. This provides forimage adjustment for both horizontal and vertical axis image skewing ofa scan image.

In the alternate embodiment of FIG. 4, the image sensor 26 is coupled totwo separate linear actuators 52, 54 for movement and rotation of theimage sensor 26. Both linear actuators 52, 54 include an associated LVDT56, 58 or an equivalent device for generating position feedback data.The LVDTs 56, 58 may be positioned on either side of their associatedactuators 52, 54. The first linear actuator 54 is coupled to the topleft corner of the image sensor 26 and the second linear actuator 52 isconnected to the top right corner of the image sensor 26. Preferably,both linear actuators 52, 54 operate together to move the image sensor26 about the two axes 59, 69; operating in the same direction forhorizontal axis 69 rotation of the sensor surface 26 a and in differentdirections for vertical axis 59 rotation.

In operation, a reflected image from the surface 10 of an object 2travels through the lens system 22 along an optical path as generallyindicated by 55 in FIG. 4. Where an area image sensor is used, thelength of the optical path is increased or shortened via a mirror systemas discussed above in connection with FIG. 2 to focus the image in thecenter of the sensor surface 26 a. The movable mirror system is notnecessary where a linear image sensor is used as discussed below inconnection with FIG. 5.

Vertical axis skewing is adjusted for by displacing actuators 52, 54 inopposite directions to tilt the sensor surface 26 a along the verticalaxis 59. Horizontal axis image skewing is adjusted for by controllingthe actuators 52, 54 in tandem to pivot the sensor surface 26 a abouthorizontal axis 69. The LVDTs associated with both the mirror actuatorand the sensor actuators provide feedback data to assure precisefocusing of the image on sensor surface 26 a.

With reference to FIG. 5, there is shown an additional embodiment of thesupplemental automatic focusing control, similar to the embodimentdepicted in FIG. 4, but specifically directed to the use of a linearimage sensor. As with the embodiment depicted in FIG. 4, two linearactuators 52, 54 are provided with associated LVDTs 56, 58 foroperationally displacing the sensor surface 26 a along a verticallyoriented axis 59 and a horizontally oriented axis 69. The sensor 26 isconfigured with a centrally located linear image sensor 68 through whichthe optical axis passes. Where a linear image sensor is used, it is notnecessary to incorporate a moveable mirror in the optical path 55, sincethe optical path length focusing can be accomplished through thepivoting about the horizontal axis 69.

In operation, the sensor surface 26 a is displaced via the actuators 52,and 54 as discussed above in connection with FIG. 4. The optical path 55is lengthened and shortened by operation of the actuators 52, 54 in thesame direction.

While the embodiments of the invention have been described in detail,the invention is not limited to the specific embodiments described abovewhich should be considered as merely exemplary. Further modificationsand extensions of the present invention may be developed, and all suchmodifications are deemed to be within the scope and spirit of thepresent invention as defined by the appended claims and all legalequivalents thereto.

1. An optical scanning apparatus for scanning a surface of an objectcomprising: a conveyor for transporting an object into a scanning zone;an image sensor having a sensor plane and an image data output; anoptics system defining an optical path having an axis and a first endwhereat the object surface is locatable in the scanning zone forscanning and a second end at said sensor plane; an object positionsensor that provides skew information of an object traveling on theconveyor; and at least one linear actuator operatively coupled to theimage sensor to pivot the image sensor plane along a vertical image axisand a horizontal image axis to control the orientation of the imagesensor plane relative to the optical path axis such that when an objectsurface is located at the first end of the optical path at anorientation skewed from a plane orthogonal with the optical path axis atsaid first path end, the at least one linear actuator orients the sensorplane to a corresponding skewed orientation relative to a planeorthogonal with the optical path axis at said second path end.
 2. Theapparatus of claim 1 wherein the at least one linear actuator is coupledto a position feedback mechanism which outputs data to assist in thecontrol of the at least one linear actuator.
 3. The apparatus of claim 1wherein the at least one linear actuator comprises a first and a secondlinear actuator coupled to said image sensor for working cooperativelyto pivot the image sensor plane along the vertical image axis and thehorizontal image axis.
 4. The apparatus of claim 3 wherein one of thepivot axes of the image sensor plane is a central axis of the imagesensor plane and the optical path is configured such that said opticalpath axis passes through said central axis.
 5. The apparatus of claim 4wherein the linear actuators are coupled to respective position feedbackmechanisms which output data to assist in the control of the linearactuators.
 6. The apparatus of claim 4 wherein the image sensor is a CCDor CMOS area sensor.
 7. The apparatus of claim 4 wherein the imagesensor is a CCD or CMOS linear image sensor.
 8. An apparatus accordingto claim 1 wherein the optics system comprises: a lens subsystem; atleast one movable mirror for adjusting the length of the optical path;and a mirror linear actuator coupled to the movable mirror such thatmovement of the mirror adjusts the focus of an optical image on theimage sensor.
 9. The apparatus of claim 8 wherein at least one of the atleast one linear actuator and the mirror linear actuator are coupled toposition feedback mechanisms which output data to assist in the controlof the linear actuators.
 10. The apparatus of claim 8 wherein the imagesensor is a CCD or CMOS area sensor.
 11. The apparatus of claim 8wherein the image sensor is a CCD or CMOS linear image sensor.
 12. Theapparatus of claim 8 wherein the at least one linear actuator comprisesa first and a second linear actuator coupled to said image sensor forworking cooperatively to pivot the image sensor plane along the verticalimage axis and the horizontal image axis.
 13. The apparatus of claim 12wherein one of the pivot axes of the image sensor plane is a centralaxis of the image sensor plane and the optical path is configured suchthat said optical path axis passes through said central axis.
 14. Theapparatus of claim 13 wherein the at least one linear actuator and themirror linear actuator are coupled to respective position feedbackmechanisms which output data to assist in the control of the linearactuators.
 15. The apparatus of claim 13 wherein the image sensor is aCCD or CMOS area sensor.